A chance discovery in a Polish quarry speeds up evolution by 18 million years but the scientists who previously found the reigning stars of paleontology in the Canadian Arctic aren't ready to concede.

A fossilized footprint dating back some 397 million years and found in south central Poland, is seen on display at the Geology Institute in Warsaw. (Jan. 7, 2010)

By:Lesley Ciarula TaylorStaff Reporter, Published on Tue Jan 12 2010

A chance discovery in a Polish quarry speeds up evolution by 18 million years but the scientists who previously found the reigning stars of paleontology in the Canadian Arctic aren't ready to concede.

"This upsets the apple cart," admits Dr. Per Ahlberg, lead author of the report in the current Nature in an interview with the Star. "These are some of the most exciting fossils I have ever encountered.

Ahlberg, an evolutionary biologist at the University of Uppsala, and his Polish colleagues uncovered secure -- meaning clearly evident -- footprints of a trackway, or walking stride, of tetrapods, four-legged animals with obvious legs and feet. That means we crawled out of the water and started walking 397 million years ago, 18 million years before the previous best evidence.

"I sat there and in the course of a single afternoon found myself revising my entire understanding of my own field of research," said Ahlberg. He told the rest of the team: "This is going to be in the textbooks."

"These were tetrapods with real limbs with digits. I hit the roof when I saw what they found." Ahlberg had been called in by his former graduate student, Grzegorz Niedzwiedzki, now scientific director of the Polish Geological Institute in Warsaw.

"I don't think he could quite believe it. I mean, it's not even his subject and he's found the equivalent of Tutankhamun's tomb."

Maybe, but not so fast, said Dr. Edward Daeschler, an evolutionary biologist with the Academy of Natural Sciences in Philadelphia. Daeschler, Dr. Neil Shubin and Farish Jenkins discovered skeletons in Nunavut of Tiktaalik roseae, the link between fish and animals that walked on four legs. Tiktaalik, called the most exciting find in a decade, was a transitional creature – but it was still a fish.

"The shine on Tiktaalik has not been diminished at all," Daeschler said Tuesday from his office. "It's still the best example." Their discovery was published in Nature in 2006.

By "best" he means the Nunavut discovery included a skeleton; the Polish one does not.

"The race is on to find skeletons," said Ahlberg. "But I think it is a mistake to regard footprints as less secure than a skeleton. When you drop dead, you will leave one skeleton but millions of footprints."

Ahlberg said their evidence, uncovered between 2002 and 2008, proves "without any question, this was a walking trackway. We can see where the sediment oozed from the side of their feet when they stepped down. We can see the anatomical details of their feet."

Daechler doesn't see it. "These are isolated footprints, not in trackways. They're very large. This would be an animal that was 10-foot long. This doesn't fit my image of the way this would work. There is room for error here."

He objects to the "definitive tone" Ahlberg and his colleagues take in their research paper, but admits the discovery of a tetrapod skeleton as old as the footprints would convince him.

"Who could argue?" He's prepared to hedge his bets. "This may be the beginning of a new paradigm. The rocks are firmly dated."

While Nature has been "very supportive," launching its first issue of the year with the Polish discovery and an accompanying video, Ahlberg understands his colleagues' skepticism. "They don't know what to make of this because it changes everything."

Bones, he knows, will shut them up. "There's not much to argue about when you have the footprints and the skeleton. There they are. They existed."

But not yet. Daeschler isn't ready to concede. "These look like toes, but you can come up with other explanations. They are notoriously difficult to interpret."

Tiktaalik is derived from the Inuktitut, the name for a large, freshwater fish seen in the shallows that were related to the cod.

The Polish discovery doesn't just rewrite the history of evolution. It also challenges why we first slunk out of the sea.

"This is about more than just footprints. We're taking about moving from one living environment to another," said Ahlberg.

"We've argued until now that tetrapods were linked to the ecosystem, which was a seriously barren mud bank. This means they had nothing to do with the terrestrial ecosystem. They were not herbivores. They had vicious, nasty looking teeth and were carnivores."

Poland itself was nearly tropical, sitting in the Southern Hemisphere on a land mass that included present day Europe, North America and Greenland wedged together.

While these crocodile-sized animals were devouring fish and jellyfish that washed up from the sea "nothing was in the sky. There were no birds yet, no winged insects, no reptiles," said Ahlberg.

"There was only the sound of wind."

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